Bomb fin structure



Jan. 18, 1949. R. A. BELL BOMB FIN STRUCTURE Filed March 30, 1944Patented Jan. 18, 1949 ES ATENT FFiCE BORE FIN STRUGTURE VaniaApplication March 30, 1944, Serial No. 528,749

'1 Claim.

This invention relates to improvements in aerial bombs and the like, andmore particularly in bombs of the type wherein the fin structure isrequired to function as an antenna for radio al paratus incorporated inthe bomb.

The vibration of the fin structure of a bomb when in flight has anappreciable effect upon the aerodynamic characteristics of the bomb.This effect is not necessarily consistent and introduces a potentialsource of error affecting bombing accuracy. In bombs incorporating radioapparatus of which the fin structure constitutes an antenna, the saidvibration may additionally seriously interfere with this specialfunction of the fin.

A principal object of this invention is to provide a fin structureconstructed in a manner to avoid or to materially reduce the aforesaidundesirable effects of fin vibration.

To this end the invention contemplates maximal reduction of vibration inthe fin structure, and modification of the character of residualvibration, so as to substantially eliminate interference with the normalfunctioning of the fin structure in the respects noted.

The invention resides further in certain structural details of animproving nature hereinafter deescribed and illustrated in the attacheddrawings, wherein Fig. 1 is a View in perspective of a fin structuremade in accordance with the invention;

Fig. 2 is a view of the fin structure in a bomb assembly, the saidstructure being shown in cross section on a line corresponding to theline 22, Fig. l, and

Fig. 3 is a sectional View on the line 33, Fig. 1.

With reference to the drawings, which illustrate a preferred embodimentof the invention, the fin structure basically is built on conventionallines. It comprises a main hub element i having a conical skirt 2 which,in assembly, fits the coned extremity 3 of the bomb casing as shown inFig. 2. Th structure also includes a secondary hub element a, which inassembly, embraces a stud 5 at the outer end of a cylindrical extension6 f the casing 3, said extension constituting, in the present instance,a housing for the radio apparatus. The collar is secured to the stud bymeans of the retaining nuts l'l. Extending radially from the collar 4 inuniformly spaced relation are four arms 8, the outer ends of the armsbeing attached to and supporting .a rectangular fin member 9. From eachcorner of the member 9 a flange l I projects outwardly and radially withrespect to the common center line of the hub elements 1 and l. Theflanges H, which form active elements of the fin structure, extend fromthe outer edge It of the fin member 9, i. e. that edge which, inassembly, is relatively remote to the bomb casing 3, to points beyondthe roximate edge ill-a of said member, and the projecting' ends of theflanges H are united to the hub element l by means of struts it. In thepresent instance, the struts l2 extend radially with respect to thecommon center line of the collars and t. This structure is made entirelyof metal, and while it is designed specifically for use with bombsincorporating radio apparatus, it corresponds basically withconventional bomb fin structure.

It has been proposed to reduce or to eliminate the objectionablevibration to which fin structures of this general type are subject, byreinforcing or strengthening the structure by additional metal to theend of obtaining greater inherent rigidity in the structure as a whole.Attempts to reduce vibration by this means have proven unsuccessful. Inaccordance with the present invention, each of the elements of the finstructure which is subject to vibration is provided superficially withone or more pads of a nonmetallic material such, for example, as wood,such pads preferably being attached at both faces of the element andbeing separated from the metallic surfaces by interposed pads of felt orlike material. Thus, with reference to the drawings, each of the sidesof the rectangular fin member 9 is provided in the present instance withtwo sets of such pads, each set including a pair of non-metallicelements l3i3, secured at the inner and outer faces respectively of thesaid sides, and two pads of felt l4 respectively interposed between theelements It and the metal faces of the fin. In the present instance theelements it and M are secured to the fin structure by means of bolts l 5which pass through the elements l3l3 and Ml4 of the respective sets andthrough the metallic Wall of the member 9. The said bolts bind theelements it solidly against the felt pads l4 and compress the latter toa fraction of their normal thickness. In the present instance, the twosets of elements l3 and H3 which are applied, as described, to each ofthe sides of the fin member 9, are arranged to afford an interveningspace, and within these spaces the struts 8 are secured to the innerfaces of the side walls.

Each of the flanges H is also provided with a set of elements Ill-l6 andl'll1 corresponding respectively to the elements I3 and M of the setspreviously described and similarly secured to the opposite sides of thefins H by means of bolts l8. Since the fin structure is to function as aradio antenna, it is desirable to electrically insulate the bolts 15 and18 from the metallic fin structure, and to this end, and as shown inFig, 3, the fins are provided with insulating washers l9 through whichthe said bolts extend.

A fin structure constituted as described above has been found relativelyfree from objectionable vibration. The reduction of vibration is due inpart to the favorable stiffness-to-mass ratio ef fected by addition tothe metal fin of the nonmetallic pad system which adds considerablestiffness With a disproportionately small increase in mass. Thus,applying the formula wherein 1 represents resonant frequency, 3

the stiffness factor, and 722 mass, it will be apparent that thefrequency of vibration will be in-- creased. Reduction of vibrationalamplitude also occurs by reason of vibration of the metal fin and of theattached pad system at different frequencies with resultant frictionalcancellation. This damping action involves both sliding and impactfriction between the surfaces of the metal fins and the opposed feltsurfaces of the pads.

It is to be noted that the pad elements 53 are formed so as to provide astreamlined contour with respect to the normal direction of movement inflight, and this streamlining is also preferably extended to the struts8 and I2. This is of advantage in reducing turbulence in the flow of airthrough and past the fin structure and is a further factor ineliminating variable conditions adversely affecting bombing accuracy.

As previously set forth, wood has been found suitable for use in the padelements i3, and

Woods of relatively great density, such as oak and gum, are desirable.Materials other than wood but having similar properties may besubstituted.

Commercial felts may be used in the pad elements M, and other paddingmaterials such as resilient rubber may be used with success. There isconsiderable permissible latitude not only as to the compositions of thepad elements, but also in the form and relative disposition of theactive elements of the fin structure.

I claim:

In an aerial bomb of the type including radio apparatus, a fin structureconstituting an antenna for said apparatus and comprising a plurality ofactive fin elements of thin metal, and vibration-inhibitin-l padssecured to the faces of said elements, said pads lending stiffness tothe said elements and being composed of wood having a stifinessto-massratio substantially in excess of that of the metal of said fin so as toincrease the stiffness-to-mass ratio of the composite fin element as aWhole.

RICHARD A. BELL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,962,202 Meredith June 12, 19341,972,005 Berbecl: Aug, 28, 1934 2,18%,145 Lambert Dec. 19, 19392,340,133 Martin Jan. 25, 1944 2,393,604 Berger Jan. 29, 1946 FOREIGNPATENTS Number Country Date 91,592 Sweden Feb. 24, 1938 505,625 GreatBritain May 11, 1939 502,711 France Feb. 27, 1920

